I'm in the middle of this book now. Halfway through it, in fact. Not with this cover, though. The edition I'm reading was printed in the 1980s, and has a photo cover of the two series heroes. The model they have as Nero Wolfe looks right, but they gave Archie Goodwin a mustache that I don't think quite fits.
Anyway, yes, I'm halfway through it, as it's a very short novel. And oh! what fun it is too. Rex Stout writes New York, it's rough spots and its police department as a contemporary Wonderland. Making Wolfe himself... I'm going to go with the Caterpillar. It's refreshing to see a series with such a willfully difficult hero.